ASTM A1085 (345 MPa) and Midwest Steel: A New Standard for Structural Efficiency
Modern construction is based on structural steel. Whether it is bridges and stadiums or skyscrapers and industrial plants, the specification you choose on steel would have a direct influence on safety, economical yield and the overall project cost. In North America, the ASTM A500 has been long established as the standard of hollow structural segments (HSS) for decades. Yet with increased engineering needs–particularly in seismic regions, and in areas where fatigue factors or failure occur–designers have sought a better, more accurate, performance-based option.
In 2013, Enter ASTM A1085. Minimum yield strength (345 MPa or 50 ksi), restricted maximum strength, reduced tolerances and required toughness features characterize A1085, a grade that is expected to raise the bar of structural design applications of HSS. Although suppliers like Midwest Steel & Aluminum carry some A500 products, the introduction of A1085 come with their opportunities and challenges to those engineers, fabricators, and project managers work.
This paper discusses different aspects of development, advantages, and uses of ASTM A1085, differences between ASTM A1085 and A500, as well as the Midwest Steel in their support of designers who prefer to use this more recent specification..
Evolution of ASTM A1085
Long popular as a workhorse HSS specification was ASTM A500. It was adaptable, very usable, and cost effective. But there are disadvantages to A500. The yield strength depends upon the grade, and the standard permits a reduction in the wall thickness up to 10 percent, thus engineers have to design conservatively, instead of using the nominal properties of sections. Besides, no toughness test is necessary under A500, and there is ambiguity over the structures subject to dynamic or low-temperature loadings.
Aware of these shortcomings, industry organizations (such as the Steel Tube Institute and, through its HSS Marketing Committee, AISC) have advocated an updated standard. The outcome was ASTM A1085 and that is concentrated on consistency, efficiency and performance under stressing conditions.
Key Features of ASTM A1085 (345 MPa)
1. Controlled Yield Strength
ASTM A1085 requires a minimum yield strength of 345 MPa (50 ksi) and sets a maximum of 485 MPa (70 ksi). This upper limit reduces uncertainty in design, particularly for seismic applications where over-strength factors influence detailing and member sizing. Engineers can design more efficiently, knowing that steel strength will not exceed a predictable range.
2. Tightened Tolerances
Unlike A500, which permits a wall thickness reduction of 10%, A1085 restricts wall thickness variation to –5% and introduces a –3.5% mass tolerance. This improvement allows engineers to use the full nominal wall thickness when calculating section properties, translating to more efficient designs with less material waste.
3. Mandatory Toughness
A1085 includes a Charpy V-Notch toughness requirement of 25 ft-lb at 40 °F. This ensures fracture resistance, especially in colder climates or fatigue-sensitive structures like bridges and seismic frames. A500 has no such requirement, leaving performance to chance in critical applications.
4. Heat Treatment Option
Supplement S1 of A1085 allows optional heat treatment to relieve residual stresses caused by cold forming. This process can improve stub column compressive strength and overall ductility, offering even greater reliability for demanding structural systems.
Practical Advantages in Structural Design
Seismic Applications
Because A1085 caps yield strength at 70 ksi, seismic over-strength factors are lower and more predictable, leading to significant cost savings in detailing connections and foundations. Designers can be confident in how HSS members will behave under extreme events.
Fatigue Resistance
The Charpy toughness requirement gives A1085 a clear edge for fatigue-critical structures such as long-span bridges or high-cycle dynamic systems. This toughness improves safety and extends the service life of structures subject to repetitive stress.
Material Savings
By eliminating the need to reduce wall thickness in calculations, engineers can often select smaller or lighter sections while maintaining equivalent performance. This reduces steel tonnage, lowering both material costs and embodied carbon.
Predictability in Fabrication
Fabricators appreciate A1085’s precision. Tighter tolerances make it easier to cut, weld, and assemble members, reducing rework and improving fit-up accuracy.
ASTM A1085 vs. ASTM A500
| Feature | ASTM A500 | ASTM A1085 (345 MPa) |
| Yield Strength | 42–50 ksi (varies by grade) | 50 ksi min, 70 ksi max |
| Wall Thickness Tolerance | –10% | –5% |
| Mass Tolerance | None | –3.5% |
| Charpy Toughness | Not required | Required (25 ft-lb @ 40 °F) |
| Section Properties | Reduced for design | Full nominal usable |
| Availability | Widely stocked | On-demand, limited stocking |
While A1085 outperforms A500 in nearly every technical aspect, its adoption has been slow due to limited production runs and supply chain habits.
Availability and Supply Challenges
One of the key hurdles to broader adoption is availability. ASTM A500 is stocked nationwide and available in nearly every shape and size. In contrast, ASTM A1085 is generally produced on demand. Rolling mills only manufacture it when customers place sufficient orders to justify production.
For project managers and engineers, this means that specifying A1085 requires early planning. Design teams should consult availability charts from producers such as Atlas Tube or use the Steel Tube Institute’s HSS Capability Tool to confirm whether desired sizes can be obtained in the required timeline.
Midwest Steel and ASTM A1085
Midwest Steel & Aluminum is one of the nation’s largest independent metal service centers, known for its broad inventory of structural and specialty steels. The company supplies a wide range of HSS, primarily to ASTM A500 specifications, which remain the industry standard for most commercial and industrial projects.
Although Midwest Steel does not typically stock A1085, it plays a crucial role in connecting engineers and fabricators with mills capable of producing it. For customers requiring A1085:
- Midwest can coordinate custom orders with producers.
- The company offers logistics support, ensuring that on-demand production integrates smoothly with construction schedules.
- Engineers benefit from Midwest’s technical assistance, helping determine whether A1085 is the right fit versus more readily available A500.
In short, Midwest Steel functions as a bridge between the specification and the supply chain, making A1085 a viable option for projects that demand its higher performance.
Case Applications
1. Bridges
Bridges in cold climates benefit from the toughness requirements of A1085. Using A1085 reduces fracture risk and extends service life under fatigue loading from traffic.
2. Seismic Structures
High-rise buildings or industrial plants in seismic regions can take advantage of A1085’s capped strength and toughness, enabling efficient seismic detailing.
3. Long-Span Trusses
Large trusses for stadiums or arenas rely on consistent HSS performance. A1085 ensures predictability, reducing risk during fabrication and erection.
Economic Considerations
While A1085 may carry a higher initial cost due to limited production runs, it often pays back in efficiency savings:
- Reduced tonnage lowers steel and transportation costs.
- Predictable behavior cuts down on over-design in seismic detailing.
- Improved toughness reduces maintenance and retrofit costs over the life of the structure.
For owners focused on long-term value and resilience, these benefits outweigh modest increases in procurement costs.
Conclusion
ASTM A1085 is a gamechanger as regards to hollow structural sections. It offers an option that gives engineers a required specification, balancing between power and specifications, strength, and safety having a minimum yield strength of 345 MPa, close tolerances, and hardness requirements to use optionally, heat treatment.
Where ASTM A500 is not the intended standard, such as where seismic performance, fatigue, and material efficiency is paramount, some projects have looked to A1085. Although these applications are currently small in number, it appears that in the future these applications will grow.
The role of suppliers such as Midwest Steel & Aluminum in assisting the industry to make the transition will be critical- in associating with mills, liaising with designers, and secondarily in ensuring that designers have acceptable access to the higher-performing steel.